Converted alternator from Valeo to Bosch, still doesn't charge

Hola guys, I'm always on the X5, M5 and 740iL forums since those are the cars I ahve, so I'm just here posting this for a buddy since we're stumped at to what to do next and would appreciate your help in any way.

Roughly a week ago the battery light come on in his '00 323ci, limping it home to the point where the headlights were dimming and the dash was lite up light a Christmas tree. We read here that the Valeo regulator isn't replaceable, yet the Bosch version is. We also read there that they're physically the same alternator, so he decided to switch to the Bosch alternator since it has a replaceable regulator in case anything happens down the road.

Other than a single bushing that needed to be moved back about 1/8 to 1/4 of an inch, it dropped in perfectly and the harness plug was the same. Once we started the car, I confirmed that I had 14v at the battery and also confirmed the same at the jump start posts inside the engine bay. While he was driving the car home, everything seemed fine, yet it's doing the same thing again where eventually everything dimmed and died again. The battery is fine because it takes and holds a charge and allows his to drive around for about a half an hour or so, but the second we disconnect the battery, the car dies.

He pulled every fuse inside the glovebox, confirmed it wasn't popped, then replaced them all. Oddly, if we charge the battery and start the car, the battery light comes on, yet if I disconnect the harness, the battery light will shut off. At this point we're at a total loss and not sure what is the next step to take.

So is this really that taboo of a subject? I can't be the only one who's done this.

As for what we've tried, we removed the regulator and the two spring loaded fingers that contact the alternator are plenty long. Using Torque and my OBDII device, I'm reading around 12.2v when running, but it's still slowly trickling down.